Staphylococcus Aureus

Staphylococcus Aureus

S. aureus
is a bacterium with strains that are capable of
producing a highly heat-stable protein toxin that causes illness in
humans. Staphylococcal food poisoning (staphyloenterotoxicosis;
staphyloenterotoxemia) is the name of the condition caused by the
enterotoxins which some strains of
S. aureus
produce.

What are the symptoms of staphylococcal food poisoning?

The onset of symptoms in staphylococcal food poisoning is
usually rapid and in many cases acute. Severity of symptoms depend
on individual susceptibility to the toxin, the amount of
contaminated food eaten, the amount of toxin in the food ingested,
and the general health of the victim. The most common symptoms are
nausea, vomiting, retching, abdominal cramping, and prostration.
Some individuals may not always demonstrate all the symptoms
associated with the illness. In more severe cases, headache, muscle
cramping, and transient changes in blood pressure and pulse rate
may occur. Recovery generally takes two days, However, it us not
unusual for complete recovery to take three days and sometimes
longer in severe cases.

How is staphylococcal food poisoning diagnosed?

In diagnosing staphylococcal foodborne illness, it is important
that victims be interviewed and data gathered and analyzed.
Suspected foods should be collected and examined for
staphylococci
. The presence of relatively large numbers of
enterotoxigenic
staphylococci
is good circumstantial
evidence that the food contains toxin. The most conclusive test is
the linking of an illness with a specific food. In cases where
multiple foods are suspected, confirmation is obtained from the
detection of the toxin in the food sample(s). In cases where the
food may have been treated to kill the
staphylococci
, as in
pasteurization or heating, direct microscopic observation of the
food may be an aid in the diagnosis.

What foods are associated with staphylococcal food
poisoning?

Foods that are frequently implicated in staphylococcal food
poisoning include:

Foods that require considerable handling during preparation and
that are kept at slightly elevated temperatures after preparation
are frequently involved in staphylococcal food poisoning.
Staphylococci
exist in air, dust, sewage, water, milk, and
food or on food equipment, environmental surfaces, humans, and
animals. Humans and animals are the primary reservoirs.
Staphylococci
are present in the nasal passages and throats
and on the hair and skin of 50 percent or more of healthy
individuals. This incidence is even higher for those who associate
with or who come in contact with sick individuals and hospital
environments. Although food handlers are usually the main source of
food contamination in food poisoning outbreaks, equipment and
environmental surfaces can also be sources of contamination with
S. aureus
. Human intoxication is caused by ingesting
enterotoxins produced in food by some strains of
S. aureus
,
usually because the food has not been kept hot enough (60°C,
140°F, or above) or cold enough (7.2°C, 45°F, or
below).

How common is staphylococcal food poisoning?

The true incidence of staphylococcal food poisoning is unknown
for a number of reasons, including:

Poor responses from victims during interviews with health
officials

Misdiagnosis of the illness, which may have similar symptoms to
other types of food poisoning (such as vomiting caused by
Bacillus cereus
toxin)

Inadequate collection of samples for laboratory analyses

Improper laboratory examination.

How serious is staphylococcal food poisoning?

Death from staphylococcal food poisoning is very rare, although
such cases have occurred among the elderly, infants, and severely
debilitated persons.

Who is susceptible to staphylococcal food poisoning?

All people are believed to be susceptible to this type of
bacterial intoxication; however, intensity of symptoms may
vary.

Example of a typical outbreak

1,364 children became ill out of a total of 5,824 who had eaten
lunch served at 16 elementary schools in Texas. The lunches were
prepared in a central kitchen and transported to the schools by
truck. Epidemiological studies revealed that 95% of the children
who became ill had eaten a chicken salad. The afternoon of the day
preceding the lunch, frozen chickens were boiled for 3 hours. After
cooking, the chickens were deboned, cooled to room temperature with
a fan, ground into small pieces, placed into l2-inch-deep aluminum
pans and stored overnight in a walk-in refrigerator at
42-45°F. The following morning, the remaining ingredients of
the salad were added and the mixture was blended with an electric
mixer. The food was placed in thermal containers and transported to
the various schools at 9:30 AM to 10:30 AM, where it was kept at
room temperature until served between 11:30 AM and noon.

Bacteriological examination of the chicken salad revealed the
presence of large numbers of
S. aureus
. Contamination of the
chicken probably occurred when it was deboned. The chicken was not
cooled rapidly enough because it was stored in l2-inch-deep layers.
Growth of the staphylococcus probably occurred also during the
period when the food was kept in the warm classrooms. Prevention of
this incident would have entailed:

Screening the individuals who deboned the chicken for carriers
of the
staphylococcus

More rapid cooling of the chicken

Adequate refrigeration of the salad from the time of
preparation to its consumption

Source:

Food and Drug
Administration, January 1992

Please be aware that this information is provided to supplement the care
provided by your physician. It is neither intended nor implied to be a
substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER
IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the
advice of your physician or other qualified health provider prior to
starting any new treatment or with any questions you may have regarding a
medical condition.